1. Field of the Invention
This invention relates to a process for mining coal with a heated basic aqueous fluid to form coalate, and removing the coalate from the coal formation.
2. Prior Art
It is generally known that coal is removed from the ground using two methods, either strip mining, in which the coal is merely dug out of the ground by mechanical or hydraulic means and transferred to the place of use, or underground mining using methods such as slurry mining (see U.S. Pat. No. 3,260,548 to Reichl), room and pillar, or longwall. The means for taking the coal out of the ground in the room and pillar or longwall methods are generally mechanical cutters, rippers, planers, loaders, etc. In slurry mining hydraulic apparatus is used to direct pressurized water at the coal seam to disaggregate the coal and form a slurry which is then pumped out of the mine to the surface. In all of these coal mining techniques it is first necessary to loosen the coal from the formation using some means such as explosives, hydraulic pressure, or physically contacting the coal with cutters, etc., before the coal can be transported away from the mine and to the place of use. Such methods require much time and large capital outlays for expensive loosening equipment.
Attempts have been made in the coal industry to find an agent which would attack the coal in such a way that the bonds between the coal constituents would be weakened and mechanical separation of the coal could be facilitated. Such a process is taught by U.S. Pat. No. 1,532,826 to Lessing, wherein the coal is treated with an acid or an aryl amine to facilitate mechanical segregation of the coal. Although such an acid treatment facilitates disaggregation by mechanical means the treatment does not result in complete disaggregation of the coal. Somewhat greater disaggegation of coal by solutions containing sodium hydroxide, among other constituents, is taught by U.S. Pat. No. 3,815,826 to Aldrich et al.
It has now been discovered that by contacting a coal formation of high oxygen content coal with a heated basic aqueous solution, particularly sodium hydroxide, the coal can be substantially dissolved. Although it has been generally known that finely ground bituminous coal can be treated with an aqueous alkali solution at elevated temperatures to obtain a coke-like residue, and that the hydrogenation of these residues forms products which are more hydrocarbon-like in nature than does a similar hydrogenation of the coal itself, (see for example "Action of Aqueous Alkali on a Bituminous Coal" by Leo Kasehagen in Industrial and Engineering Chemistry, May, 1937), it was surprising indeed to discover that coal of relatively high oxygen content may be mined when contacted with a heated basic aqueous solution and dissolved in situ. This phenomena can be utilized to remove a complete coal formation more easily than the coal could be mechanically removed or removed by slurry mining. Further, the basic aqueous solution can be regenerated with an agent such as an acid or base.